Control apparatus for electric vehicles

ABSTRACT

In a hybrid vehicle control apparatus, a motor control unit executes a system voltage stabilization control, in which an input power to a MG unit is controlled to suppress variations in the system voltage. The motor control unit executes the input power control on the MG unit independently from a torque control on an AC motor so that the input power control and the torque control are stabilized. Before a smoothing capacitor is sufficiently, a conversion voltage control is executed to control an output voltage of a voltage booster converter while prohibiting the system voltage stabilization control. After the pre-charging of the capacitor, the conversion voltage control is changed to the conversion power control.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by referenceJapanese Patent Applications No. 2006-89713 filed on Mar. 29, 2006 andNo. 2006-309076 filed on Nov. 15, 2006.

This application is related to US patent applications (IPICS 99951-USand 101862-US) claiming priorities to the following Japanese PatentApplications, respectively:

-   No. 2005-343750 filed on Nov. 29, 2005; and-   No. 2006-40272 filed on Feb. 17, 2006.

FIELD OF THE INVENTION

The present invention relates to a control apparatus for an electricvehicle including a system for converting a voltage generated by a DCpower supply into a system voltage by using a voltage converter and fordriving an AC motor by applying the system voltage to the AC motorthrough an inverter.

BACKGROUND OF THE INVENTION

As disclosed in documents such as U.S. 2006/0052915A1 (JP 2004-274945A),in an electric vehicle having AC motors mounted therein to serve as apower source of the vehicle, the AC motors are each capable of servingas a motor for driving wheels of the vehicle as well as a motor drivenby an engine to generate power. As the above system, a control apparatusfor the electric vehicle includes a voltage boosting converter forraising a voltage generated by a DC power supply, which is implementedby a secondary battery, to a high DC voltage appearing on a power supplyline connected to the AC motors through inverters. The inverters arecapable of serving as a component for converting the raised DC voltageappearing on the power supply line into an AC voltage for driving one ofthe AC motors as well as a component for converting the AC voltage intoa DC voltage supplied back or restored to the secondary battery throughthe voltage boosting converter, which lowers the level of the DCvoltage.

In the above system, in order to stabilize the voltage appearing on thepower supply line, the voltage boosting converter controls the voltageappearing on the power supply line to a target voltage. Further, at thesame time, a smoothing capacitor connected to the power supply linesmoothes the voltage appearing on the power supply line.

When a relation between electric power driving one of the AC motors andelectric power generated by the other AC motor considerably varies dueto a change in vehicle operating state or another reason, however,voltage variations caused by a change in such relation as voltagevariations of the power supply line cannot be absorbed by the voltageboosting converter and/or the smoothing capacitor. Thus, the voltageappearing on the power supply line becomes excessively high. As aresult, it is likely that electronic equipment connected to the powersupply line is damaged. In order to cope with this problem, there isprovided a method for enhancing the effect of stabilizing the voltageappearing on the power supply line by using an improved voltage boostingconverter with better performance and a smoothing capacitor with alarger capacitance. By adoption of this method, however, the voltageboosting converter with better performance and the smoothing capacitorwith a larger capacitance will inevitably raise the cost of the controlapparatus for an electric vehicle. Thus, demands for a system having asmall size and a low cost cannot be met. The above relation between thepower driving one of the AC motors and the power generated by the otherAC motor is also referred to as a balance of power between the powerdriving one of the AC motors and the power generated by the other ACmotor.

It is proposed for controlling the inverter to make a sum of energies(or balance of electric power) of the two AC motors equal to 0 at thetime the connection between the DC power supply and the voltage boostingconverter is cut off by using a relay in the event of a failureoccurring in the DC power supply. However, this method is provided as acountermeasure to a failure occurring in the DC power supply and iscapable of enhancing the effect of stabilizing the voltage appearing onthe power supply line in a normal state of the power supply. Inaddition, even if an attempt is made to control the inverter to make thesum of energies (or the balance of power) of the two AC motors equal to0 in a normal state, it is difficult to control the inverter to make thesum of energies (or the balance of power) of the two AC motors equal to0 in the following cases.

In the first place, one of the AC motors is linked to a driving shaft ofthe electric vehicle and the other AC motor is linked to an output shaftof the internal combustion engine, that is, the two AC motors are linkedto members having different operations. In the second place, the effectof a processing delay of the control executed on the inverter becomeslarger, for example, during a transient in which the operating state ofthe electric vehicle changes. The AC motor linked to the internalcombustion engine is not capable of obviating power variations caused bychanges of a torque generated by the internal combustion engine. Thisfact makes it even more difficult to control the inverter to make thesum of energies of the two AC motors equal to 0.

SUMMARY OF THE INVENTION

It is thus an object of the present invention to improve a controlapparatus for electric vehicles to be capable of stabilizing a voltageappearing on a power supply line in small size and low cost.

According to one aspect, a control apparatus for an electric vehiclecomprises a conversion unit that converts a voltage supplied by a DCpower supply into a system voltage appearing on a power supply line, andan MG unit that includes an inverter connected to the power supply lineand drives an AC motor. The control apparatus controls a torque of theAC motor and an input electric power to the MG unit independently fromeach other, executes a system voltage stabilization control to controlthe input electric power to the MG unit so as to suppress variation inthe system voltage by sending a command value for controlling the inputelectric power, executes a conversion power control to control aconversion power, which is an input electric power or an output power ofthe converter means from the converter means, and executes a conversionvoltage control to control the voltage. The control apparatus selectsexecution of either the conversion power control or the conversionvoltage control, and inhibits execution of the system voltagestabilization control when the conversion voltage control is selected.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a block diagram showing a driving system for an electricvehicle in accordance with an embodiment of the present invention;

FIG. 2 is a block diagram showing one part of a control system employedin the driving system for controlling AC motors of the driving system inaccordance with the embodiment;

FIG. 3 is a block diagram showing the other part of the control systememployed in the driving system for controlling AC motors of the drivingsystem in accordance with the embodiment;

FIG. 4 is a graph showing a characteristic of a current vector used forcomputing a command current vector in the embodiment;

FIG. 5 is a block diagram showing a second current control part in theembodiment;

FIG. 6 is a graph showing method of calculating detected current vectorsfor torque control and input power control in the embodiment; and

FIG. 7 is a flowchart showing main processing of motor control in theembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, an electric vehicle 11 has an internalcombustion engine 12 in addition to a first AC motor 13 and a second ACmotor 14. Thus, the electric vehicle 11 is an engine/motor hybridvehicle. The engine 12 and the second AC motor 14 are employed as adrive power source for driving the electric vehicle 11. Power generatedby a crankshaft 15 of the engine 12 is divided into two paths by aplanetary gear set 16. The planetary gear set 16 includes a sun gear 17,a planetary gear 18 and a ring gear 19. The sun gear 17 rotates at itsradial center. The planetary gear 18 rotates along a circumferenceexternal to the sun gear 17 while revolving around its radial center.The ring gear 19 rotates along a circumference external to the planetarygear 18. The planetary gear 18 is linked to the crankshaft 15 of theengine 12 through a carrier not shown in the figure. On the other hand,the ring gear 19 is linked to a rotation shaft of the second AC motor14. The sun gear 17 is linked to the first AC motor 13.

A secondary battery serving as a DC power supply 20 is connected to avoltage boosting converter 21 serving as a power conversion means. Thevoltage boosting converter 21 is a component having a function forincreasing a DC voltage output by the DC power supply 20 in order togenerate a DC system voltage supplied between a power supply line 22 anda ground line 23 as well as a function for decreasing the system voltagein order to return or restore power to the DC power supply 20. Asmoothing capacitor 24 for smoothing the system voltage and a voltagesensor 25 serving as a voltage detection means for detecting a value ofthe system voltage are connected between the power supply line 22 andthe ground line 23. A current sensor 26 serving as a current detectionmeans is placed on the power supply line 22 as a means for detecting acurrent flowing through the power supply line 22.

In addition, a three-phase first inverter 27 and a three-phase secondinverter 28 are also connected between the power supply line 22 and theground line 23. The three-phase first inverter 27 and the three-phasesecond inverter 28 are each a three-phase inverter of a voltage controltype. The three-phase first inverter 27 drives the first AC motor 13,whereas the three-phase second inverter 28 drives the second AC motor14. The three-phase first inverter 27 and the first AC motor 13 form afirst motor driving unit 29, which operates as a first MG unit 29.Similarly, the three-phase second inverter 28 and the second AC motor 14form a second motor driving unit 30, which operates as a second MG unit30.

A main control unit 31 is a computer for executing overall control onthe electric vehicle as a whole. The main control unit 31 acquiressignals output by a variety of sensors and switches in order to detectan operating state of the electric vehicle. The sensors and the switchesinclude an accelerator sensor 32, a shift switch 33, a brake switch 34and a vehicle speed sensor 35. The accelerator sensor 32 is a sensor fordetecting an accelerator operation quantity representing an operationquantity of an acceleration pedal. The shift switch 33 is a sensor fordetecting gear shift position of the electric vehicle. The gear shiftposition can be a parking position (P), a rear driving position (R), aneutral position (N) or a forward driving position (D). The brake switch34 is a switch for detecting a braking operation. The vehicle speedsensor 35 is a sensor for detecting a value of the travel speed of theelectric vehicle. The main control unit 31 exchanges control and datasignals with an engine control unit 36 and a motor control unit 37,driving the engine control unit 36 and the motor control unit 37 tocontrol the engine 12, the first AC motor 13 and the second AC motor 14in accordance with the operating state of the electric vehicle. Theengine control unit 36 is for controlling the operation of the engine12, whereas the motor control unit 37 is for controlling the operationsof the first AC motor 13 and the second AC motor 14.

Next, control of the first AC motor 13 and the second AC motor 14 isdescribed by referring to FIGS. 2 and 3. The first AC motor 13 and thesecond AC motor 14 are each a three-phase permanent-magnet synchronousmotor having a permanent magnet in its inside. The first AC motor 13 andthe second AC motor 14 have respectively rotor rotational positionsensors 39 and 40 each used for detecting the rotational position of therotor of the motor. On the basis of three-phase voltage command signalsUU1, UV1 and UW1 output by the motor control unit 37, the first inverter27 of the voltage control type converts the DC system voltage appearingon the power supply line 22 into three-phase AC voltages U1, V1 and W1for driving the first AC motor 13. The DC system voltage appearing onthe power supply line 22 is generated by the voltage boosting converter21. A U-phase current sensor 41 is a sensor for detecting a U-phasecurrent iU1 of the first AC motor 13, whereas a W-phase current sensor42 is a sensor for detecting a W-phase current iW1 of the first AC motor13.

Similarly, on the basis of three-phase voltage command signals UU2, UV2and UW2 output by the motor control unit 37, the three-phase secondinverter 28 of the voltage control type converts the DC system voltageappearing on the power supply line 22 into three-phase AC voltages U2,V2 and W2 for driving the second AC motor 14. A U-phase current sensor43 is a sensor for detecting a U-phase current iU2 of the second ACmotor 14, whereas a W-phase current sensor 44 is a sensor for detectinga W-phase current iW2 of the first AC motor 13.

It is to be noted that the first AC motor 13 and the second AC motor 14each also function as an electric power generator, when the first ACmotor 13 and the second AC motor 14 are driven by the three-phase firstinverter 27 and the three-phase second inverter 28 respectively togenerate a negative torque. For example, when the electric vehicle 11 isbeing decelerated, AC power generated by the second AC motor 14 as adeceleration energy is converted into DC power by the three-phase secondinverter 28 and the DC power is accumulated back in the DC power supply20. Normally, a portion of power of the engine 12 is transferred to thefirst AC motor 13 by way of the planetary gear 18, causing the first ACmotor 13 to operate as a generator for generating electric powercorresponding to the portion of the power of the engine 12. The electricpower generated by the first AC motor 13 is supplied to the second ACmotor 14, causing the second AC motor 14 to operate as a motor. Thepower of the engine 12 is divided into two paths by the planetary gearset 16. When a torque applied to the ring gear 19 of the planetary gearset 16 is greater than a torque required by a running operation of theelectric vehicle, the first AC motor 13 functions as a motor, drawingpower for the engine 12. In this case, the second AC motor 14 functionsas a generator generating power to be supplied to the first AC motor 13.Thus, each of the first AC motor 13 and the second AC motor 14 operatesas a motor/generator (MG).

At the start of operating the vehicle drive system (at the operationstart of the main control unit 31 or the motor control unit 37), themotor control system is in a state of being shut down (motor control andthe like have been halted) and almost no electric charge has beenaccumulated in the smoothing capacitor 24. Prior to starting the motorcontrol, therefore, it is necessary to pre-charge the smoothingcapacitor 24 to elevate the system voltage up to a target value.

Therefore, the motor control unit 37 executes a main motor controlprogram shown in of FIG. 7 that will be described later. That is, rightafter the start of system operation but before the smoothing capacitor24 has been sufficiently pre-charged, the motor control unit 37selectively executes the conversion voltage control to control theoutput voltage of the voltage boosting converter 21 so that the systemvoltage is quickly brought into agreement with the target value. Duringexecution of this conversion voltage control, the motor control unit 37further prohibits the electric power command value (input poweroperation quantity Pm) for stabilizing the system voltage that will bedescribed later from being output to an input electric power system(input electric power control current computation unit 54 to therebyprohibit the execution of control for stabilizing the system voltage.After the smoothing capacitor 24 has been pre-charged, a pre-chargecompletion signal is transmitted to the main control unit 31.

When it is so determined on the basis of the pre-charge completionsignal and other signals that the motor control system may be releasedfrom the shut-down state, the main control unit 31 transmits a readysignal to the motor control unit 37.

Upon receipt of the ready signal, the motor control unit 37 releases themotor control system from the shut-down state, executes the motorcontrol, discontinues the conversion voltage control, and changes thecontrol over to the conversion power control. Thus, the motor controlunit 37 controls the output power of the voltage boosting converter 21so that the output voltage of the voltage boosting converter 21 isbrought into agreement with the command value.

In the motor control, the control unit 37 executes the torque controlfor controlling the torque of the first AC motor 13, the torque controlfor controlling the torque of the second AC motor 14, and the systemvoltage stabilization control for controlling the input power of thesecond AC motor 30 so that variation in the system voltage may besuppressed. The control unit 37 executes the torque control for thesecond AC motor 14 and the input power control for the second MG unit 30independently from each other.

The motor control unit 37 executes the motor control (torque control,system voltage stabilization control), the conversion voltage controland the conversion power control as described below.

(Motor Control)

The motor control unit 37 executes motor control (torque control, MGpower control and system voltage stabilization control) as well as theconversion voltage control and conversion power control.

When the smoothing capacitor 24 has been sufficiently pre-charged, thatis, pre-charging the smoothing capacitor 24 has been completed, afterthe start of system operation, the motor control unit 37 releases themotor control system from the shut-down state and executes the motorcontrol (torque control, system voltage stabilization control).

In execution of torque control on the first AC motor 13, the motorcontrol unit 37 generates the three-phase voltage command signals UU1,UV1 and UW1 by a sinusoidal-waveform PWM control method on the basis ofa torque command value T1* output by the main control unit 31, theU-phase current iU1 and W-phase current iW1 of the first AC motor 13 aswell as the rotor rotational position θ1 of the first AC motor 13 asdescribed below. The U-phase current iU1 and the W-phase current iW1 aresignals output by the current sensors 41 and 42 respectively, whereasthe rotor rotational position θ1 is a signal output by the rotorrotational position sensor 39.

The signal output by the rotor rotational position sensor 39 as a signalrepresenting the rotor rotational position θ1 of the first AC motor 13is supplied to a first rotation speed computation unit 45 for computinga first rotation speed N1 of the first AC motor 13. Then, in order toapply current feedback control to each of a d-axis current id1 and aq-axis current iq1 independently of each other in a d-q coordinatesystem set as a rotational coordinate system of the rotor of the firstAC motor 13, a first torque control current computation unit 46 computesa torque control current vector it1* representing a d-axis torquecontrol current idt1* and a q-axis torque control current iqt1* by usingtypically map data or a mathematical equation as a vector according tothe torque command value T1* and rotation speed N1 of the first AC motor13.

Subsequently, a first current vector control unit 47 computes an actualcurrent vector i1 (d-axis current id1 and the q-axis current iq1) on thebasis of the U-phase current iU1 and W-phase current iW1 of the first ACmotor 13 as well as the rotor rotational position θ1 of the first ACmotor 13 as described below. As described above, the U-phase current iU1and the W-phase current iW1 are signals output by the current sensors 41and 42 respectively, whereas the rotor rotational position θ1 is thesignal output by the rotor rotational position sensor 39. Then, thefirst current vector control unit 47 computes a d-axis command voltageVd1* by execution of P-I control for reducing a difference Δid1 betweenthe d-axis torque control current idt1* and an actual d-axis currentid1, and computes a q-axis command voltage Vq1* by execution ofproportional-and-integral (P-I) control for reducing a difference Δiq1between the q-axis torque control current iqt1* and an actual q-axismotor detection current iq1. Finally, the first current vector controlunit 47 converts the d-axis command voltage Vd1* and the q-axis commandvoltage Vq1* into the three-phase PWM command signals UU1, UV1 and UW1,outputting the three-phase PWM command signals UU1, UV1 and UW1 to thethree-phase first inverter 27.

Thus, the torque control for controlling the torque of the first ACmotor 13 is executed to realize the torque command value T1* output bythe main control unit 31.

In execution of torque control on the second AC motor 14, on the otherhand, the motor control unit 37 generates the three-phase voltagecommand signals UU2, UV2 and UW2 by the sinusoidal-waveform PWM controlmethod on the basis of a torque command value T2* output by the maincontrol unit 31, the U-phase current iU2 and W-phase current iW2 of thesecond AC motor 14 as well as the rotor rotational position θ2 of thesecond AC motor 14. As described below, the U-phase current iU1 and theW-phase current iW1 are signals output by the current sensors 43 and 44respectively, whereas the rotor rotational position θ1 is a signaloutput by the rotor rotational position sensor 40.

At this time, control of stabilizing the system voltage is executed inorder to suppress variations in the system voltage while sustaining thetorque generated by the second AC motor 14 at a constant value (torquecommand value T2*) by adjusting an input power to the second AC motor 14through adjustment of a current vector so as to change only the inputpower (or reactive power) different from the power required forgeneration of the torque of the second AC motor 14.

Specifically, first of all, the signal output by the rotor rotationalposition sensor 40 as a signal representing the rotor rotationalposition θ2 of the second AC motor 14 is supplied to a second rotationspeed computation unit 48 for computing a rotation speed N2 of thesecond AC motor 14. Then, in order to apply current feedback control toeach of a d-axis current id2 and a q-axis current iq2 independently ofeach other in a d-q coordinate system set as a rotational coordinatesystem of the rotor of the second AC motor 14, a second torque controlcurrent computation unit 49 computes a torque control current vectorit2* representing a d-axis torque control current idt2* and a q-axistorque control current iqt2* by using typically map data or amathematical equation as a vector according to a torque command valueT2* and rotation speed N2 of the second AC motor 14.

Then, a system voltage target value computation unit 50 serving as atarget value computation means computes a target value Vs* of the systemvoltage, whereas the voltage sensor 25 supplies a detection value Vs ofthe system voltage to a first low pass filter 51 serving as a firstlow-frequency component passing means for carrying out a low passfiltering process to pass only components included in the detectionvalue Vs of the system voltage as components each having a lowfrequency. Subsequently, a subtractor 52 computes a difference ΔVsbetween the target value Vs* of the system voltage and a detection valueVsf output by the low pass filtering process as the detection value ofthe system voltage, supplying the difference ΔVs to the a P-I controller53 serving as a power operation quantity computation means for computingan input power operation quantity Pm of the second AC motor 14 as aquantity that reduces the difference ΔVs between the target value Vs* ofthe system voltage and the detection value Vsf output by the low passfiltering process as the detection value of the system voltage byexecution of P-I control.

The input electric power operation amount Pm is input to aninhibit/permit gate 72. Upon receipt of a ready signal from the maincontrol unit 31, the input electric power operation amount Pm ispermitted to be output to an input electric power control currentcomputation unit 54. Upon inputting the input electric power operationamount Pm to the input electric power control current computation unit54, a command current vector ip2* (d-axis command current idp2*, q-axiscommand current iqp2*) for controlling the input electric power iscomputed in a manner as described below to vary the reactive power thatdoes not contribute to producing the torque of the second AC motor 14 bythe input electric power operation amount Pm as shown in FIG. 4.

First, the d-axis command current idp2* for controlling the inputelectric power which is dependent upon the input electric poweroperation amount Pm and upon the command current vector it2* (d-axiscommand current idt2*, q-axis command current iqt2*) for controlling thetorque, is computed by using a map or a numerical formula, and theq-axis command current iqp2* for controlling the input electric power isoperated by using the d-axis command current idp2* for controlling theinput electric power.i iqp2*=[(Ld−Lq)×idp2*×iqt2*]/[(Ld−Lq)×(idp2*+idt2*)+φ]

where φ is a magnetic flux linkage, Ld is a d-axis inductance, and Lq isa q-axis inductance, which are device constants of the AC motor 14.

Thus, the command current vector ip2* (d-axis command current idp2*,q-axis command current iqp2*) for controlling the input electric poweris computed to vary the input electric power (reactive power) to thesecond AC motor 14 by the input electric power operation amount Pm whilemaintaining the torque of the second AC motor 14 (torque command valueT2*) constant.

Thereafter, the command current vector it2* (d-axis command currentidt2*, q-axis command current iqt2*) for controlling the torque and thecommand current vector ip2* (d-axis command current idp2*, q-axiscommand current iqp2*) for controlling the input electric power, areinput to a second current control unit 55 (current control means) shownin FIG. 5. In this second current control unit 55, a coordinateconverter unit 73 computes a motor detection current vector i2 (d-axismotor detection current id2, q-axis motor detection current iq2) whichis a detected value of current actually flowing into the second AC motor14 based on the currents iU2 and iW2 of U-phase and W-phase of thesecond AC motor 14 (output signals of the current sensors 43 and 44) andon the rotational position θ2 of the rotor of the second AC motor 14(output signal of the rotor rotational position sensor 40).

Thereafter, in order to control the torque of the second AC motor 14 andto control the electric power input to the second AC motor 14independently from each other, a current separation unit 74 (currentseparation means) separates the detected motor current vector i2 (d-axisdetected motor current id2, q-axis detected motor current iq2) into adetected current vector it2 (d-axis detected current idt2, q-axisdetected current iqt2) for controlling the torque related to the torquecontrol and a detected current vector ip2 (d-axis detected current idp2,q-axis detected current iqp2) for controlling the input electric powerrelated to the input electric power control.

FIG. 6 shows a method of separating the detected motor current vector i2into the detected current vector it2 for controlling the torque and thedetected current vector ip2 for controlling the input electric power.Here, ω denotes an electric angular velocity, L denotes an inductance, Rdenotes an armature winding resistance and φ denotes an interlinkingmagnetic flux. The motor command voltage vector V2* is a voltage vectorobtained by adding a command voltage vector Vp2* for controlling theinput electric power to the command voltage vector Vt2 for controllingthe torque, and the voltage vector V0 is a voltage vector computed bymultiplying the electric angular velocity ω by the magnetic flux linkageφ.

At a moment when the phase difference is α between the voltage vector(V2*−V0) and the current vector i2, and R and ωL are not almostchanging, a triangle A formed by the three current vectors i2, it2 andip2 is similar to a triangle B formed by the three voltage vectors(V2*−V0), (Vt2*−V0) and Vp2*. Therefore, the similarity ratio R of thetriangle A by the current vectors to the triangle B by the voltagevectors becomes a value obtained by dividing the length of the currentvector i2 by the length of the voltage vector (V2*−V0),R=|i2|/|V2*−V0|

That is, the triangle A formed by the three current vectors i2, it2 andip2 is a triangle which works to advance the angle by α in the directionof each side of the triangle B formed by the three voltage vectors(V2*−V0), (Vt2*−V0) and Vp2*, and to lengthen each side by R times.

It is, therefore, allowed to compute the detected current vector it2(d-axis detected current idt2, q-axis detected current iqt2) forcontrolling the torque by computing a vector that advances the angle byα in the direction of the voltage vector (Vt2*−V0) and lengthens thelength thereof by R times. It is, further, allowed to compute thedetected current vector ip2 (d-axis detected current idp2, q-axisdetected current iqp2) for controlling the input electric power byfinding a vector that advances the angle by α in the direction of thevoltage vector Vp2* and lengthens the length thereof by R times.

After the detected motor current vector i2 is separated into thedetected current vector it2 for controlling the torque and the detectedcurrent vector ip2 for controlling the input electric power, asubtractor 75 computes a difference Δidt2 between the d-axis commandcurrent idt2* for controlling the torque and the d-axis detected currentidt2 as shown in FIG. 5. The difference Δidt2 is input to a P-Icontroller 76 which computes a d-axis command voltage Vdt2* forcontrolling the torque by the P-I control so that the difference Δidt2decreases. Further, a subtractor 77 computes a difference Δiqt2 betweenthe q-axis command current iqt2* for controlling the torque and theq-axis detected current iqt2, and the difference Δiqt2 is input to a P-Icontroller 78 which computes a q-axis command voltage Vqt2* forcontrolling the torque by the P-I control so that the difference Δiqt2decreases. Thus, a command voltage vector Vt2* (d-axis command voltageVdt2*, q-axis command voltage Vqt2*) for controlling the torque iscomputed to decrease the difference between the command current vectorit2* for controlling the torque and the detected current vector it2.

Further, a subtractor 79 computes a difference Δidp2 between the d-axiscommand current idp2* for controlling the input electric power and thed-axis detected current idp2, and the difference Δidp2 is input to a P-Icontroller 80 which computes a d-axis command voltage Vdp2* forcontrolling the input electric power by the P-I control so that thedifference Δidp2 decreases. Further, a subtractor 81 computes adifference Δiqp2 between the q-axis command current iqp2* forcontrolling the input electric power and the q-axis detected currentiqp2, and the difference Δiqp2 is input to a P-I controller 82 whichcomputes a q-axis command voltage Vqp2* for controlling the inputelectric power by the P-I control so that the difference Δiqp2decreases. Thus, a command voltage vector Vp2* (d-axis command voltageVdp2*, q-axis command voltage Vqp2*) for controlling the input power iscomputed to decrease the difference between the command current vectorip2* for controlling the input electric power and the detected currentvector ip2.

As described above, the command voltage vector Vt2* (d-axis commandvoltage Vdt2*, q-axis command voltage Vqt2*) for controlling the torqueand the command voltage vector Vp2* (d-axis command voltage Vdp2*,q-axis command voltage Vqp2*) for controlling the input electric power,are independently computed. Thereafter, an adder 83 adds the d-axiscommand voltage Vdp2* for controlling the input electric power to thed-axis command voltage Vdt2* for controlling the torque to compute afinal d-axis motor command voltage Vd2*, while an adder 84 adds theq-axis command voltage Vqp2* for controlling the input electric power tothe q-axis command voltage Vqt2* for controlling the torque to compute afinal motor q-axis command voltage vector Vq2*. Thus, the motor commandvoltage vector V2* (d-axis motor command voltage Vd2, q-axis motorcommand voltage Vq2*) is determined. V2* (d-axis motor command voltageVd2, q-axis motor command voltage Vq2*) is converted through acoordinate converter unit 85 into three-phase voltage command signalsUU2, UV2 and UW2, which are output to a second inverter 28 of thesethree-phase voltage command signals UU2, UV2 and UW2.

As described above, the system voltage stabilization control is executedto suppress variation in the system voltage by executing the torquecontrol to control the torque of the second AC motor 14 so as to realizethe torque command value T2* output from the main control unit 31, byexecuting the input electric power control to vary the electric power(reactive power) input to the second AC motor 14 by the input electricpower operation amount Pm while maintaining the torque of the second ACmotor 14 (torque command value T2*) constant, and by so controlling theelectric power input to the second MG unit 30 (second AC motor 14) thatthe difference ΔVs decreases between the target value Vs* of the systemvoltage and the detected value Vsf. In this case, the P-I controller 53,the input electric power control current computation unit 54 and thelike units operates as system voltage control means.

(Conversion Voltage Control)

Right after the start of system operation but before completion ofpre-charging the smoothing capacitor 24, the motor control unit 37executes the conversion voltage control to control the output voltage ofthe voltage boosting converter 21 so as to decrease the difference ΔVsbetween the target value Vs* and the detection value Vsf of the systemvoltage.

Specifically referring to FIG. 3, the system voltage target valuecomputation unit 50 computes the target value Vs* of the system voltage,the system voltage Vs detected by the voltage sensor 25 is input to thefirst low pass filter 51 to execute the low pass filtering processpermitting the passage of components in a low-frequency region only ofthe detected system voltage Vs. Thereafter, a subtractor 68 computes thedifference ΔVs between the target value Vs* of the system voltage andthe detection value Vsf of the system voltage after being subjected tothe low pass filtering. The difference ΔVs is input to a P-I controller69 (conversion voltage control quantity computing means), and a currentduty ratio Dvc of a switching element that is not shown in the voltageboosting converter 21 is computed by P-I control so as to decrease thedifference ΔVs between the target value Vs* of the system voltage andthe detection value Vsf of the system voltage after being subjected tothe low pass filtering.

The current duty ratio Dvc for voltage control and the current dutyratio Dpc for power control that will be described later are input to avoltage boosting drive selection and computation unit 70, which operatesas a selector means. After the start of the system, the voltage boostingdrive selection and computation unit 70 determines whether the readysignal from the main control unit 31 has been received. When it isdetermined that the ready signal has not been received, it is sodetermined that the smoothing capacitor 24 has not yet been sufficientlypre-charged, and the current duty ratio Dvc for voltage control isselected as a current duty ratio Dc of the switching element in thevoltage boosting converter 21 to thereby execute the conversion voltagecontrol by the voltage boosting converter 21.Dc=Dvc

Thereafter, a voltage boosting drive signal computation unit 71 computesvoltage boosting drive signals UCU, UCL based on the current duty ratioDc (=Dvc) for power control, and the voltage boosting drive signals UCUand UCL are output to the voltage boosting converter 21.

Right after the start of system operation but before the smoothingcapacitor 24 has been sufficiently pre-charged, the conversion voltagecontrol is executed to control the output voltage of the voltageboosting converter 21 so as to decrease the difference ΔVs between thetarget value Vs* and the detection value Vsf of the system voltage. Thesmoothing capacitor 24 is, thereafter, sufficiently pre-charged so thatthe system voltage is quickly controlled to become the target value.During this conversion voltage control, the system voltage control(system voltage stabilization control) by operating the input power ofthe second MG unit 30 is prohibited. As a result, interference betweenthe system voltage control (system voltage stabilization control) andthe system voltage control (conversion voltage control) is restricted.In this case, the P-I controller 69, the voltage boosting driveselection and computation unit 70 and the voltage boosting drive signalcomputation unit 71 operate as a conversion voltage control means.

(Conversion Power Control)

After the start of system operation and the smoothing capacitor 24 hasbeen sufficiently pre-charged, the motor control unit 37 halts the aboveconversion voltage control, and changes the operation over to conversionpower control to control the output voltage of the voltage boostingconverter 21 so as to decrease the difference ΔPi between the commandvalue Pif* and the detection value Pi of electric power output by theboosting converter 21.

When the command value Pif* of electric power output from the boostingconverter 21 is to be computed, first, the torque command value T1* andthe rotational speed N1 of the first AC motor 13 are input to a firstshaft output computation unit 56 to compute a shaft output PD1 of thefirst AC motor 13. Further, the torque command value T1* and therotational speed N1 of the first AC motor 13 are input to a first outputloss computation unit 57 to compute an output loss PL1 of the first ACmotor 13. Thereafter, an adder 58 adds the output loss PL1 to the shaftoutput PD1 of the first AC motor 13 to compute an input power Pi1 to thefirst AC motor 13. In this case, when the first AC motor 13 is operatingas a generator, the computation result of input power Pi1 to the firstAC motor 13 assumes a negative value.

Further, the torque command value T2* and the rotational speed N2 of thesecond AC motor 14 are input to a second shaft output computation unit59 to operate a shaft output PD2 of the second AC motor 14. Further, thetorque command value T2* and the rotational speed N2 of the second ACmotor 14 are input to a second output loss computation unit 60 tocompute an output loss PL2 of the second AC motor 14. Thereafter, anadder 61 adds the output loss PL2 to the shaft output PD2 of the secondAC motor 14 to compute an input power Pi2 to the second AC motor 14. Inthis case, when the second AC motor 14 is operating as a generator, thecomputation result of input power Pi2 to the second AC motor 14 assumesa negative value.

Thereafter, the input power Pi1 to the first AC motor 13 and the inputpower Pi2 to the second AC motor are added up together through an adder62 to compute a total electric power Pi*. The total electric power Pi*is input to a second low pass filter 63 (second low frequency componentpassing means) so as to be subjected to the low pass filtering processpermitting the passage of components in a low-frequency region only ofthe total electric power Pi*. The total electric power Pif* after beingsubjected to the low pass filtering is regarded to be the command valuePif* for the conversion power. The adder 62 and the second low passfilter 63 operate as conversion power command value computation means.

When a detection value Pi of electric power output from the voltageboosting converter 21 is to be computed, a detection value ic of currentoutput from the voltage boosting converter 21 detected by the currentsensor 26 is input to a third low pass filter 64 (third low frequencycomponent passing means) and is subjected to the low pass filteringprocess permitting the components in the low-frequency region only topass through in the detection value ic of current output from thevoltage boosting converter 21. A conversion power detection unit 65multiplies the target value Vs* of the system voltage by the detectionvalue icf of current output from the voltage boosting converter 21 afterhaving been subjected to the low pass filtering in order compute adetection value Pi of the conversion power. The detection value Vsf ofthe system voltage may be multiplied by the detection value icf of theoutput current to compute the detection value Pi of the output power.

Thereafter, a difference ΔPi between the command value Pif* and thedetection value Pi of electric power output from the voltage boostingconverter 21 is computed by a subtractor 66. The difference ΔPi is inputto a P-I controller 67 (conversion power control amount computationmeans), and a current duty ratio Dpc of a switching element (not shown)in the voltage boosting converter 21 is computed by P-I control so as todecrease the difference ΔPi between the command value Pif* and thedetection value Pi of electric power output from the voltage boostingconverter 21.

The current duty ratio Dpc for power control and the current duty ratioDvc for voltage control are input to the voltage boosting driveselection and computation unit 70, which operates as a selection means.The voltage boosting drive selection and computation unit 70 determinesif the ready signal from the main control unit 31 has been receivedafter the start of the system. When it is determined that the readysignal has been received already, it is so determined that the smoothingcapacitor 24 has been pre-charged, and the current duty ratio Dpc forpower control is selected as a current duty ratio Dc for the switchingelement in the voltage boosting converter 21 so as to execute theconversion power control by the voltage boosting converter 21.Dc=Dpc

Thereafter, based on the current duty ratio Dc (=Dpc) for power control,the voltage boosting drive signal computation unit 71 computes voltageboosting drive signals UCU and UCL, and outputs the voltage boostingdrive signals UCU and UCL to the voltage boosting converter 21.

After the smoothing capacitor 24 has been pre-charged as describedabove, the conversion power control is executed to control the electricpower output from the voltage boosting converter 21 so as to decreasethe difference ΔPi between the command value Pif* and the detectionvalue Pi of electric power output from the voltage boosting converter21. Thus, the electric power supplied to the power line 22 by thevoltage boosting converter 21 can be controlled as desired. In thiscase, the P-I controller 67, the voltage boosting drive selection andcomputation unit 70 and the voltage boosting drive signal computationunit 71 operate as a conversion power control means.

The above motor control (torque control, system voltage stabilizationcontrol), conversion voltage control and conversion power control areexecuted according to a main motor control program shown in FIG. 7. Thisprogram is repetitively executed at a predetermined interval after thestart of system operation. When the program starts, it is determined atstep 101, first, if the ready signal is received from the main controlunit 31. When it is determined that the ready signal has not beenreceived, it is so determined that the smoothing capacitor 24 has notbeen sufficiently pre-charged yet. The routine proceeds to step 102,where the conversion voltage control is executed to so control theoutput voltage of the voltage boosting converter 21 that the differenceΔVs between the target value Vs* and the detection value Vsf of thesystem voltage decreases. As a result, the smoothing capacitor 24 ispre-charged to quickly control the system voltage so as to assume thetarget value. While the conversion voltage control at step 102 is beingexecuted, the system voltage control (system voltage stabilizationcontrol at step 105) by computing the input power to the second MG unit30 is prohibited.

The routine, thereafter, proceeds to step 103 to determine whether thesmoothing capacitor 24 has been sufficiently pre-charged. When it isdetermined that the pre-charging the smoothing capacitor 24 has beencompleted (sufficiently pre-charged), the routine proceeds to step 104where a pre-charge completion signal is transmitted to the main controlunit 31.

When it is determined based on the pre-charge completion signal or othersignals that the motor control system needs no longer be placed in theshut-down state, the main control unit 31 transmits the ready signal tothe motor control unit 37.

Thereafter, when it is determined at step 101 that the ready signal isreceived from the main control unit 31, it is so determined that thesmoothing capacitor 24 has been sufficiently pre-charged. The routinethen proceeds to step 105 where the motor control system is no longerplaced in the shut-down state, and the motor control (torque control,system voltage stabilization control) is executed. At step 106, theconversion voltage control is changed over to the conversion powercontrol, and the output power of the voltage boosting converter 21 is socontrolled as to decrease the difference ΔPi between the command valuePif* and the detection value Pi of the electric power output from thevoltage boosting converter 21.

According to the above embodiment, the input power to the second MG unit30 (second AC motor 14) is so controlled that the difference ΔVsdecreases between the target value Vs* and the detection value Vsf ofthe system voltage to execute the system voltage stabilization controlin order to suppress variation in the system voltage of the power supplyline 22. Therefore, even when the power balance greatly varies betweenthe two AC motors 13 and 14 due to changes in the operating conditionsof the vehicle, the system voltage can be effectively stabilized.Besides, the voltage of the power supply line 22 can be highlystabilized without using the voltage boosting converter 21 of highperformance or without using the smoothing capacitor 24 of a largecapacity, satisfying the requirement of realizing the system in a smallsize and at a decreased cost.

In this embodiment, further, the detected motor current vector i2 isseparated into a detected current vector it2 for controlling the torqueand the detected current vector ip2 for controlling the input electricpower, the command voltage vector Vt2* is computed for controlling thetorque so that the difference decreases between the command currentvector it2* for controlling the torque and the detected current vectorit2, and the command voltage vector Vp2* is computed for controlling theinput electric power so that the difference decreases between thecommand current vector ip2* for controlling the input electric power andthe detected current vector ip2. Then, the command voltage vector Vt2*for controlling the torque and the command voltage vector Vp2* forcontrolling the input electric power are computed independently fromeach other. The final motor command voltage is computed based upon thecommand voltage vector Vt2* for controlling the torque and on thecommand voltage vector Vp2* for controlling the input electric power tothereby control the torque of the second AC motor 14 and the electricpower input to the second MG unit 30 independently from each other. Thisprevents the interference between controlling the torque of the secondAC motor 14 and controlling the electric power input to the second MGunit 30, and helps stabilize the torque control for the second AC motor14 and the input electric power control for the second MG unit 30.

In this embodiment, further, right after the start of system operationbut before the smoothing capacitor 24 has been sufficiently pre-charged,the conversion voltage control is executed to so control the outputvoltage of the voltage boosting converter 21 that the difference ΔVsdecreases between the target value Vs* and the detection value Vsf ofthe system voltage. The smoothing capacitor 24 is, thereafter,pre-charged to quickly control the system voltage so as to assume thedesired value. Besides, the power command value (input power operationquantity Pm) for stabilizing the system voltage is prohibited from beinginstructed to the motor control to thereby prohibit the execution of thesystem voltage stabilization control. Next, after the smoothingcapacitor 24 has been pre-charged, the motor control system is no longerplaced in the shut-down state, and the motor control system is releasedfrom the shut-down state. Thus, the motor control (torque control,system voltage stabilization control) is started, and the conversionvoltage control is changed over to the conversion power control. As aresult, the output power of the voltage boosting converter 21 is socontrolled that the difference ΔPi decreases between the command valuePif* and the detection value Pi of the electric power output from thevoltage boosting converter 21. Thus, the conversion voltage control andthe conversion power control are changed over depending upon theconditions of the vehicle. Besides, when the conversion voltage controlis being executed, execution of the system voltage stabilization controlis prohibited. Therefore, the system voltage can be effectivelystabilized without being affected by the conditions of the vehicle.

Further, in the above embodiment, the system controls the second ACmotor 14 by the sinusoidal wave PWM control method, wherein, instabilizing the system voltage, the current vector is so controlled asto vary only the reactive power that does not contribute to producingthe torque of the second AC motor 14 to thereby control the systemvoltage by controlling the input power to the second AC motor 14, whilemaintaining the torque of the second AC motor 14 constant (at the torquecommand value T2*). Therefore, variation in the system voltage can besuppressed without adversely affecting the operating condition of thevehicle.

In this embodiment, further, the input power operation quantity Pm forthe second AC motor 14 is computed by using the detection value Vsf ofsystem voltage after having been subjected to the low pass filtering. Atthe time of computing the input power operation quantity Pm, therefore,the detection value Vsf of system voltage can be used after the noisecomponents (high-frequency components) included in the detection valueVs of system voltage have been removed through low pass filtering, andthe accuracy in computing the input power operation quantity Pm can beimproved.

According to this embodiment, the command value Pif* for the conversionpower is computed from the total electric power Pi* obtained by addingup the power Pi1 input to the first AC motor 13 and the power Pi2 inputto the second AC motor. Further, the target value Vs* (or detectionvalue Vsf) of the system voltage is multiplied by the detection valueicf of the current output from the voltage boosting converter 21 tocompute the detection value Pi of the conversion power. Further, theelectric power output from the voltage boosting converter 21 is socontrolled as to decrease the difference ΔPi between the command valuePif* and the detection value Pi of the conversion electric power. Whenthe conversion power control is to be executed, the system voltagecontrol (system voltage stabilization control) by operating the electricpower input to the second MG unit 30 is prohibited. Thus, the electricpower supplied to the power supply line 22 can be controlled as desired,the system voltage can be stabilized, reducing the burden on theconversion of power caused by the system voltage control (system voltagestabilization control) by operating the electric power input to thesecond MG unit 30.

In this embodiment, further, the total power Pif* after the total powerPi* of power Pi1 input to the first AC motor 13 and power Pi2 input tothe second AC motor is subjected to the low pass filtering process, isused as the command value Pif* for the conversion power. Therefore, thetotal electric power Pif* after the noise components (high-frequencycomponents) are removed by low pass filtering can be used as the commandvalue Pif* for the conversion power, making it possible to accuratelyset the command value Pif* for the conversion power. Besides, uponlimiting the frequency band, the voltage boosting converter 21 can beprevented from operating at high speeds, and the voltage boostingconverter 21 of low performance having a small size can be used, whichis advantageous for being mounted on a vehicle.

In this embodiment, further, the detection value Pi of conversion poweris operated by using the detection value icf of current output from thevoltage boosting converter 21 after having been subjected to the lowpass filtering. In computing the detection value Pi of conversion power,therefore, there can be used the detection value icf of output currentafter noise components (high-frequency components) included in thedetection value ic of output current have been removed by low passfiltering to improve accuracy for operating the detection value Pi ofconversion power.

At the start of the electric vehicle, further, the system voltage,usually, starts with zero. A predetermined target voltage must beattained to complete the start. In this case, the MG unit 30 has beenshut down in the initial stage of start, and the system voltagestabilization cannot be executed by using the MG unit 30. To cope withthis, at the start of the electric vehicle, this embodiment does notexecute the conversion power control but executes the conversion voltagecontrol, instead, while prohibiting the system voltage control (systemvoltage stabilization control) which is based on operating the electricpower input to the MG unit 30. This prevents the system voltage control(system voltage stabilization control) based on the operation of powerinput to the MG unit 30 from interfering with the system voltage control(conversion power control) by the voltage boosting converter 21, andmakes it possible to effectively stabilize the system voltage and tosmoothly start the electric vehicle.

After the start of the electric vehicle, the MG unit 30 may often beoverheated due to abnormal condition in the cooling system while theelectric vehicle is traveling. In this case, the MG unit 30 may often beshut down to protect the MG unit 30. In this case, therefore, the systemvoltage stabilization cannot be executed by using the MG unit 30.

To cope with this, therefore, in case the MG unit 30 is overheated dueto abnormal condition in the cooling system while the electric vehicleis traveling, this embodiment does not execute the conversion powercontrol but executes the conversion voltage control, instead, whileprohibiting the system voltage control (system voltage stabilizationcontrol) which is based on the operation of electric power input to theMG unit 30. Thus, the system voltage is controlled by controlling thevoltage by using the voltage boosting converter 21, the system voltageis effectively stabilized, the system voltage is prevented from becomingexcessive, and the MG unit 30 and the like are reliably protected.

In the above embodiment, the AC motors are controlled by the sinusoidalPWM control method. However, the system may control the AC motors basedon any other control systems (e.g., rectangular wave control system).

In the above embodiment, further, the electric power output from thevoltage boosting converter 21 is so controlled as to decrease thedifference ΔPi between the command value Pif* and the detection value Piof electric power output from the voltage boosting converter 21 at thetime of controlling the conversion electric power. However, it is alsopossible to so control the electric power input to the voltage boostingconverter 21 as to decrease the difference ΔPi between the command valuePif* and the detection value Pi of electric power input to the voltageboosting converter 21.

In the above embodiment, further, the electric power input to the secondMG unit 30 (second AC motor 14) is controlled to suppress variation inthe system voltage at the time of the system voltage stabilizationcontrol operation. However, variation in the system voltage may besuppressed by controlling the electric power input to the first MG unit29 (first AC motor 13). Alternatively, in a vehicle of theall-wheel-drive constitution mounting a third MG unit on the drivenwheels, variation in the system voltage may be suppressed by controllingthe electric power input to the third MG unit.

The above embodiment is directed to a hybrid vehicle of the so-calledsplit type, which splits the motive power of the engine through theplanetary gear mechanism. Not being limited to the hybrid vehicle of thesplit type, however, the embodiment may be hybrid vehicles of othertypes, such as a parallel type and a series type. In the aboveembodiment, further, the vehicle uses the AC motor and the engine asmotive power sources. However, the vehicle may use the AC motor only asa motive power source. The vehicle may have only one MG unit comprisingan inverter and an AC motor, or three or more MG units.

1. A control apparatus for an electric vehicle comprising: a conversionmeans that converts a voltage supplied by a DC power supply into asystem voltage appearing on a power supply line; an MG unit thatincludes an inverter connected to the power supply line and drives an ACmotor; a current control means for controlling a torque of the AC motorand an input electric power to the MG unit independently from eachother; a system voltage control means for executing a system voltagestabilization control to control an electric power input to the MG unitso as to suppress variation in the system voltage by sending a commandvalue for controlling the input electric power to the current controlmeans; a conversion power control means for executing a conversion powercontrol to control a conversion power, which is an input electric poweror an output power of the converter means from the converter means; aconversion voltage control means for executing a conversion voltagecontrol to control the voltage output from the converter means; and aselection means for selecting execution of either the conversion powercontrol or the conversion voltage control, and for inhibiting executionof the system voltage stabilization control when the conversion voltagecontrol is selected.
 2. The control apparatus according to claim 1,wherein the current control means computes a motor command voltage,which is a command value of voltage to be applied to the AC motor, basedupon a command voltage for controlling the torque of the AC motor and acommand voltage for controlling the input electric power to the MG unit.3. The control apparatus according to claim 2, wherein: the currentcontrol means includes a current separation means for separating adetected motor current, which is a detected value of electric currentflowing into the AC motor, into a detected current for torque controlrelated to controlling the torque of the AC motor and a detected currentfor input electric power control related to controlling the inputelectric power to the MG unit; and the current control means computes acommand voltage for torque control based on the command current forcontrolling the torque of the AC motor and on the detected current forcontrolling the torque, and further computes the command voltage forcontrolling the input electric power based on the command current forcontrolling the input electric power to the MG unit and on the detectedcurrent for controlling the input electric power.
 4. The controlapparatus according to claim 3, wherein the current separation meanscomputes a detected current for controlling the torque based on themotor command voltage, the detected motor current and the commandvoltage for controlling the torque.
 5. The control apparatus accordingto claim 3, wherein the current separation means computes a detectedcurrent for controlling the input electric power based on the motorcommand voltage, the detected motor current and the command voltage forcontrolling the input electric power.
 6. The control apparatus accordingto claim 1, further comprising: a target voltage-setting means forsetting a target value of the system voltage; and a voltage detectionmeans for detecting the system voltage, wherein the system voltagecontrol means computes the input electric power operation amount for theMG unit based on the target value of system voltage set by the targetvoltage-setting means and on the system voltage detected by the voltagedetection means, and sends a command value for controlling the inputelectric power to the current control means based on the input electricpower operation amount to thereby control the system voltage.
 7. Thecontrol apparatus according to claim 6, further comprising: a low-passmeans for permitting passage of components lower than a predeterminedfrequency of the system voltage detected by the voltage detection means,wherein the system voltage control means computes an input electricpower operation amount to the MG unit by using a system voltage of lowerthan the predetermined frequency that has passed through the low-passmeans.
 8. The control apparatus according to claim 1, furthercomprising: a conversion power command value computation means forcomputing a command value for the conversion power; and a conversionpower detection means for detecting the conversion power, wherein theconversion power control means computes a control amount for theconversion power based on the command value for the conversion powercomputed by the conversion power command value computation means and onthe conversion power detected by the conversion power detection means,and controls the conversion power based on the control amount for theconversion power.
 9. The control apparatus according to claim 8, whereinthe conversion power command value computation means computes a commandvalue for the conversion power based on an electric power input to allelectric loads inclusive of the MG unit connected to the power supplyline.
 10. The control apparatus according to claim 9, furthercomprising: a low-pass means for permitting passage of components lowerthan a predetermined frequency of the electric power input to allelectric loads inclusive of the MG unit connected to the power supplyline, wherein the conversion power command value computation meanscomputes a command value for the conversion power based on an electricpower of lower than the predetermined frequency that has passed throughthe low-pass means.
 11. The control apparatus according to claim 8,further comprising: at least either one of a target voltage-settingmeans for setting a target value of the system voltage or a voltagedetection means for detecting the system voltage; and a currentdetection means for detecting an output current of the converter means,wherein the conversion power detection means computes the conversionpower based on the target value of the system voltage set by the targetvoltage-setting means or a system voltage detected by the voltagedetection means and the output current of the converter means detectedby the current detection means.
 12. The control apparatus according toclaim 11, further comprising: a low-pass means for permitting passage ofcomponents lower than a predetermined frequency of the output current ofthe converter means detected by the current detection means, wherein theconversion power detection means computes the conversion power by usingan output current lower than the predetermined frequency that has passedthrough the low-pass means.
 13. The control apparatus according to claim1, further comprising: a target voltage-setting means for setting atarget value of the system voltage; and a voltage detection means fordetecting the system voltage, wherein the conversion voltage controlmeans computes the amount of controlling the output voltage of theconverter means based on the target value of the system voltage set bythe target voltage-setting means and the system voltage detected by thevoltage detection means, and controls the output voltage of theconverter means based on the amount of controlling the output voltage.